Patent Literature 1 indicates that a modulated wave is subjected to delta-sigma modulation by a band-pass delta-sigma modulator, and a quantized signal (pulse signal) outputted from the band-pass delta-sigma modulator is outputted as the modulated wave. According to Patent Literature 1, when the modulated wave is subjected to band-pass delta-sigma modulation, the sampling frequency is preferably sufficiently high with respect to the signal bandwidth of the modulated wave. Therefore, even if the frequency of the modulated wave (the frequency of a non-modulated wave) is high, the sampling frequency need not be increased so much.
Patent Literature 1 further indicates that a harmonic signal component included in the output of the delta-sigma modulator is utilized as well as a main signal component included in the output of the delta-sigma modulator. According to Patent Literature 1, by utilizing the harmonic signal component included in the output of the delta-sigma modulator, the sampling frequency of the delta-sigma modulator can be kept low.